There are two ways to obtain large discharge volumes in conventional scroll type compressors: enlarge the diameter of the movable and fixed scrolls or increase their axial lengths. In the conventional compressor as shown in FIG. 9, for reasons described below the axial length of both movable scroll 100 and fixed scroll 101 can not be extended to obtain larger discharge volumes. Hence, the diameters of both scrolls 100, 101 must be extended in order to get enough discharge volume, causing the outer diameter of the compressor to become larger. That generally causes inconvenience in putting the scroll compressor in an engine room of a car when the scroll type compressor is used as a refrigerant compressor for an automotive air conditioner. So generally an enlarged compressor is not the solution, nor is increasing the axial length of the scrolls for reasons discussed below.
As shown in FIG. 9, the movable scroll 100 orbits and compresses the refrigerant in a working chamber 102, so that a reactive force F1 results on the movable scroll 100 due to differential pressures in the different parts of the chamber between the scrolls 100 and 101. In other words, a shaft 103 rotates the movable scroll 100 by a driving force F2 against the reactive force F1. Since the working directions of forces F1 and F2 are opposite, the bending moment for movable scroll 100 increases in the clockwise direction. That moment of rotation is cancelled by the moment of rotation which is caused from the thrust reactive forces X1, X2 acting on the ball bearing type support members 104, 105. The sum of the reactive forces X1, X2 is equal to a pressing force F3 by which the refrigerant in the working chamber 102 presses the movable scroll 100. The pressing force F3 is determined according to the volume of the working chamber 102 and has an almost constant value.
However, when the axial length of the scrolls 100 and 101 is increased as shown in FIG. 10, the bending moment from forces F1, F2 increases, causing a clockwise rotation or tilt of scroll 100. This in turn increases the reactive force X1 and eliminates the reactive force X2 of FIG. 9. The pressing force which forces the movable scroll 100 into the support member 105 does not occur. Instead, the outer end of the movable scroll 100 contacts the fixed scroll 101 and a new opposite direction reactive force X2 arises due to friction at the point where the movable scroll 100 contacts the fixed scroll 101. In other words, the support member 105 moves apart from a supporting plate 106.
When the movable scroll 100 tilts into contact with the fixed scroll 101, the friction or contact pressure of the movable scroll 100 and the fixed scroll 101 becomes larger. Also, the driving force to orbit the movable scroll 100 becomes larger than an appropriate value, and the durability of the movable scroll 100 and the fixed scroll 101 becomes less. Furthermore, since the movable scroll 100 inclines or tilts due to the clockwise bending moment, a leak of refrigerant from between the movable scroll 100 and the fixed scroll 101 might occur.
Because of the reasons described above, the movable scroll 100 and the fixed scroll 101 should not be designed in such a manner that the moment comprising the reactive force Fl and the driving force F2 becomes excessively large. Consequently, in the past it has been necessary to keep the widths of the movable scroll 100 and the fixed scroll 101 relatively small, preventing the capability of handling the presently required larger volumes of fluid.